Blood pumps are indispensable for conducting extracorporeal blood circulation in an artificial heart and lung apparatus and the like. A turbo blood pump is known as one of the blood pumps. In the turbo blood pump, an impeller is rotated in a pump chamber having inlet and outlet ports to generate a differential pressure for transporting blood with a centrifugal force.
The turbo blood pump can be miniaturized and reduced in weight and cost due to the operation principle thereof. Furthermore, the turbo blood pump is excellent in durability since it is not affected by a tube damage or the like unlike a roller-pump type blood pump; therefore, the turbo blood pump can be used preferably for continuous operation for a long period of time. Thus, the turbo blood pump is becoming mainstream as a blood pump for an extracorporeal circulation circuit in an artificial heart and lung apparatus or a cardioassist apparatus after open-heart surgery.
For example, a turbo blood pump described in Patent Document 1 has a configuration shown in FIG. 6. In this figure, reference numeral 1 denotes a housing, which forms a pump chamber 2 for allowing blood to pass and flow therethrough, and is provided with an inlet port 3 that communicates with an upper portion of the pump chamber 2 and an outlet port 4 that communicates with a side portion of the pump chamber 2. In the pump chamber 2, an impeller 5 is placed. FIG. 7A is a top view of the impeller 5. The impeller 5 has six vanes 6, a rotating shaft 7, and a ring-shaped annular coupling portion 8.
As shown in FIG. 7A, the six vanes include vanes of two kinds of shapes: long main vanes 6a and short sub vanes 6b, which are placed alternately. The main vanes 6a and the sub vanes 6b are referred to as the vanes 6 collectively. Ends of the main vanes 6a on a center side are coupled to the rotating shaft 7 via arms 18, and ends thereof on a circumferential edge side are coupled to the annular coupling portion 8. The ends of the sub vanes 6b on the center side are free ends not coupled to the rotating shaft 7, and only ends thereof on the circumferential edge side are coupled to the annular coupling portion 8. The reason why all the vanes 6 are not coupled to the rotating shaft 7 is to prevent the increasing number of the arms 18 from interfering with a flow path. A minimum number of the arms 18 sufficient for transmitting the rotation of the impeller to the rotating shaft 7 may be provided. As the cross-sectional shape of the vanes 6 in FIG. 6, only those which are taken along the main vanes 6a in FIG. 7A are illustrated, for the sake of convenience.
Although not shown precisely in FIG. 7A, the vanes 6 (both the main vanes 6a and the sub vanes 6b) have a three-dimensional curved surface shape as shown in FIG. 7B. Specifically, a line segment connecting between an upper end of the vane 6 and a lower end thereof on an inlet side (center portion of the impeller 5) on which blood flowing from the inlet port 3 comes into contact with (bumps against) the vane 6 is referred to as a vane inlet line K. Further, a line segment connecting between an upper end of the vane 6 and a lower end thereof on an outlet side (outer circumferential edge portion of the impeller 5) on which blood leaves from the vane 6 is referred to as a vane outlet line L. The vane inlet line K is twisted with respect to the rotating shaft 7, and the vane outlet line L is twisted with respect to the vane inlet line K.
For example, the vane outlet line L is parallel to the direction of the rotating shaft 7, whereas an angle γ formed by the vane inlet line K with respect to the direction of the rotating shaft 7 is set to be about 30°, for example. The vane 6 formed of planes connecting the vane inlet line K to the vane outlet line L between an inlet portion and an outlet portion has a three-dimensional curved surface of a twisted shape. Thus, a blood pump with hemolysis reduced can be realized, which has a sufficient ejection ability and suppresses cavitation (peeling, whirlpool of flow) generated on the outlet side of the vane 6.
As shown in FIG. 6, the rotating shaft 7 is supported rotatably by an upper bearing 9 and a lower bearing 10 provided at a housing 1. The annular coupling portion 8 is provided with a magnet case 11 in which driven magnets 12 are embedded. Each of the driven magnets 12 has a cylindrical shape, and six driven magnets 12 are placed at a predetermined interval in a circumferential direction of the annular coupling portion 8. The annular coupling portion 8 and the magnet case 11 form a cylindrical inner circumferential surface.
A rotor 13 is placed below the housing 1. The rotor 13 includes a drive shaft 14 and a substantially cylindrical magnetic coupling portion 15, which are coupled to each other. Although not shown, the drive shaft 14 is supported rotatably, and is coupled to a rotation drive source such as a motor to be rotated. Furthermore, the relative positional relationship is kept constant between the rotor 13 and the housing 1 by an element (not shown). Drive magnets 16 are embedded in an upper surface portion of the magnetic coupling portion 15. The drive magnets 16 have a cylindrical shape, and the six drive magnets 16 are placed at a predetermined interval in a circumferential direction.
The drive magnets 16 are placed so as to be opposed to the driven magnets 12 with a wall of the housing 1 interposed therebetween. Thus, the rotor 13 and the impeller 5 are coupled to each other magnetically, and when the rotor 13 is rotated, the impeller 5 is rotated through magnetic coupling.
A surface of the annular coupling portion 8, on which the driven magnets 12 are set, is an inclined surface that is not orthogonal to the rotating shaft 7 and has a predetermined angle. Similarly, an upper surface of the magnetic coupling portion 15, on which the drive magnets 16 are set, is an inclined surface. Thus, the driven magnets 12 and the drive magnets 16 form magnetic coupling on a surface inclined with respect to the rotating shaft of the impeller 5, whereby the magnetic attractive force acting on an area between the impeller 5 and the rotor 13 is generated in a direction inclined with respect to the rotating shaft of the impeller 5. Consequently, the downward load on the lower bearing 10 is reduced. Thus, the friction of the lower bearing 10 is alleviated, so that the strength of magnetic coupling can be made sufficiently large.
As is understood from the figure, the impeller 5 has a space 19 in a region inside the annular coupling portion 8, allowing a flow path passing vertically through the vanes 6 to be formed. A base 20 having a cylindrical outer circumferential surface, which protrudes upward, i.e., to the inside of the pump chamber 2, is formed at the center in a bottom portion of the housing 1. The base 20 is formed so as to fill the space 19 in the region inside the driven magnets 12 and the annular coupling portion 8 in the lower portion of the impeller 5, which minimizes the volume of the space. Thus, the priming volume in the pump chamber 2 is reduced.
The upper bearing 9 is placed at a position below the inlet port 3, penetrating the pump chamber 2. Three bearing pillars 17 are provided on the inner surface in a lower end portion of the inlet port 3, and extend diagonally downward to penetrate the pump chamber 2, and the upper bearing 9 is supported by the tip end of the bearing pillars 17 in the center portion of the flow path cross-section of the inlet port 3. The lower bearing 10 is provided at the center in an upper surface portion of the base 20.
In the turbo blood pump with the above configuration, the impeller 5 is supported vertically by the upper bearing 9 and the lower bearing 10. Therefore, the supported state of the impeller 5 is stable, and hence, the rotation state is stable, whereby the stable blood supply can be realized. Further, the annular coupling portion 8 does not have a size covering the entire bottom surface of the housing 1, and the impeller 5 has a space in a region spreading between the rotating shaft 7 and the annular coupling portion 8. Thus, the impeller 5 is light-weight, and a small drive force suffices.
Further, the formation of a blood clot in a stagnant portion of blood is a problem caused by using the blood pump for a long time. For example, blood stagnates easily in a lower portion of an impeller of a conventional blood pump, and there is a possibility that a blood clot may be formed. However, the above-mentioned configuration disclosed by Patent Document 1 is also effective for eliminating the stagnant portion of blood. The reason for this is as follows. Since a flow path passing vertically through the vanes 6 is formed in a region spreading between the rotating shaft 7 and the annular coupling portion 8, blood flowing to the lower portion of the impeller 5 passes through the vicinity of the lower bearing 10 to reach the vanes 6 and flows out in an outer diameter direction of the vanes 6. Such a flow function suppresses the stagnation of blood.
However, in the case of the configuration of the blood pump disclosed by Patent Document 1, a number of blood clots are formed on the periphery of the rotating shaft 7, for example, in the vicinity of the lower bearing 10 on the upper surface of the base 20. As a result of an experiment, the following is found: although blood in a gap between the impeller 5 and the bottom surface of the housing 1 flows toward the center of the impeller 5, the flow rate of a blood stream becomes small in a gap portion 21 on the inner side of the annular coupling portion 8, and in particular, a blood stream at a sufficient flow rate is not formed in the vicinity of the lower bearing 10 on the upper surface of the base 20. Therefore, the blood stagnates, and the heat generated by the lower bearing 10 serves as a main factor for hemolysis. Further, due to the above-mentioned stagnation, a blood clot is formed easily in the vicinity of the lower bearing.
In order to solve the above-mentioned problems, Patent Document 2 discloses a turbo blood pump of a configuration as shown in the cross-sectional view of FIG. 8. The blood pump is different from the conventional example shown in FIG. 6 in the configuration of an impeller 22. FIG. 9 is a top view of the impeller 22, and FIG. 10 is a cross-sectional view thereof.
As is clearly shown in FIGS. 9 and 10, the impeller 22 has a blockade member 23 placed below the vanes 6 in a region spreading between the rotating shaft 7 and the annular coupling portion 8. The blockade member 23 blocks a flow path passing from a space in the region, which spreads between the rotating shaft 7 and the annular coupling portion 8, to the vanes 6, while leaving a part of an opening 24 around the rotating shaft 7. By providing the blockade member 23, the formation of a blood clot around the rotating shaft 7, for example, in the vicinity of the lower bearing 10 on the upper surface of the base 20 can be suppressed.
More specifically, by providing the blockade member 23, the blood in the gap between the impeller 22 and the bottom surface of the housing 1 flows toward the center of the impeller 5 along the lower surface of the blockade member 23, and thereafter, rises through the opening 24 of the blockade member 23. At this time, a blood stream with a sufficient flow rate is formed adjacent to the lower bearing 10 along the rotating shaft 7, which prevents the stagnation of blood. Thus, the region where blood stagnates, forming a blood clot according to the configuration of Patent Document 1, also is ready to be washed away at all times, so that the formation of a blood clot is suppressed.